Olefinic polymers such as polyethylenes, polypropylene, ethylene/α-olefin copolymers and propylene/α-olefin copolymers are widely used for various molding materials and the like. The characteristics required for these olefinic polymers differ depending on the use thereof. For example, the olefinic polymer for food use is required not to damage the taste of foods because a delicate smell and taste are regarded as important.
In the meantime, when, in the production of an olefinic polymer, olefins are polymerized by a vapor phase polymerization method in the presence of a solid state catalyst, the polymer can be obtained in the form of a particle and such as a step of precipitating a polymer and a step of separating solvents after polymerization become needless. Therefore, this is known to be able to simplify the production process and to reduce the production cost. However, the olefinic polymer produced by a vapor phase polymerization method sometimes exudes an odor when processed with heat and this may affect flavors and the like especially when the olefinic polymer is employed for food use where a delicate smell and taste are regarded as important. Therefore, the use of these polymers are occasionally limited in such uses.
As a method of reducing the influence of the odor of the olefinic polymer obtained by a vapor phase polymerization method and the influence of the olefinic polymer on taste when it is used for food uses, for example, a method is described in the publication of Japanese Patent Application Laid-Open No. 10-45824 for decreasing the odor emanated from the olefinic polymer during molding by contacting the olefinic polymer obtained using a metallocene catalyst with steam and the like to decompose the cyclopentadienyl ligand in the polymer.
Although the odor of the olefinic polymer can be considerably decreased by the method like this, it has been desired to further decrease odors in food use and the like in recent years.
In this situation, the inventors of the present invention have made studies and, consequently reached to the completion of the present invention with a finding that upon producing a olefinic polymer by a vapor phase polymerization method, the odor is greatly reduced by carrying out the polymerization reaction in the presence of a saturated aliphatic hydrocarbon in a fluidized bed reactor and then contacting the obtained polymer with steam and the like.